Fixed keels do two very basic things: provide stability, and prevent the boat from sliding to leeward when sailing upwind. There are several ways to achieve one or both of these benefits without a fixed keel, but they are all compromises, and compromises bring mixed blessings.
A centerboard configuration allows the sailboat to do things that a fixed keel would prohibit. A sailboat without a fixed keel can sit on its bottom in a vertical position (when the tide is out), instead of heeling over; it can sail much faster because of reduced wetted surface and drag; and its center of lateral resistance below the waterline can be adjusted for different points of sail. Consider that on a recently designed racing sled, the daggerboard can be used to replace a broken rudder (see Vendée Globe—Entering a New Era), and you begin to understand the value of adjustable appendages.
However, the alternatives to fixed keels bring their own set of problems. While a centerboard, swing keel, or stub keel/centerboard combination are extremely simple, fixing them is not necessarily a simple matter when something goes wrong.
It is also not a simple matter to use them. There can be many more actions to take than just raising the board while going downwind and dropping it when going to windward. For instance, by experimenting with the position of the centerboard on my catboat Kirsten, I’ve found that it’s possible to balance the tiller so she can sail herself on many points of sail.
The simplest alternatives to a fixed keel are the daggerboard and the centerboard. These provide the lateral resistance needed to prevent the boat from sliding sideways to leeward, but they are not usually ballasted and do not provide the stability that a ballasted, fixed keel offers.
Centerboards are different from daggerboards in two respects: they are housed in a casing fitted into the bilge of the boat, and they are raised and lowered by a pennant—a rope or wire—by hand or with a winch. Some boats use a more complex system involving a piston, wire pennant, turning blocks, and winch for this work. Apparently, small variations between a centerboard and a daggerboard make a world of difference when something goes wrong because most centerboards are inaccessible from inside the boat. If the rope or wire that raises and lowers it breaks, someone will have to dive in to fix it, or the boat will have to be hauled out for repair. If a piston is involved, hauling the boat out to repair the piston is nearly unavoidable.
A broken centerboard pin, a short metal rod that allows the board to pivot up and down, can be a tough or easy job to repair, depending upon its accessibility. Bronze is the best metal for the centerboard pin, especially in salt water, because stainless steel pins can suffer crevice corrosion.
When a small boat with a daggerboard capsizes, it is usually easy to right it by standing on the daggerboard and gripping the gunwale or mast. Because centerboards can pivot into a casing, care must be taken to ensure the boat doesn't turtle completely.
Because centerboards can occasionally scrape along the bottom, wearing off epoxy or fiberglass coatings, centerboards should not have steel, iron, or plywood cores that will rust or rot if exposed to water. Most centerboards can be easily repaired with fiberglass, but if a centerboard is broken beyond repair, replacement can be difficult and expensive. If the boat’s original manufacturer is no longer in business, or did not keep the original mold for the centerboard, replacing the centerboard will become a custom effort. Someone skilled in do-it-yourself work might be able to undertake it, but it may be best to seek out a boatyard that can handle the project.
Swing keels may or may not have a casing, but they are ballasted, providing additional stability that a daggerboard or centerboard cannot. This makes a broken pennant a much more serious problem, since the swing keel can be severely damaged if it runs aground, on rocks, or is deeply embedded in sand or mud, while a centerboard is usually light enough to bump harmlessly up into its casing. Diving overboard to fix or replace the pennant may be necessary to avoid more trouble.
Because stability is compromised by the use of an alternative to a fixed keel, most sailboats without fixed keels will be much wider, or beamier, to make up for the loss of the ballasted keel. This increases wetted area and drag, slowing the boat unless the bottom is flat enough to get up on a plane, in which case it can often go much faster than a boat with a fixed keel.
Boards and swing keels can take sailors up creeks and into shallow bays and, after a trailer trip, onto remote mountain lakes that are less accessible to sailors with fixed-keel boats. They may be a compromise that bars some bluewater sailing, but they open up other worlds—no small feat for something as simple as a board.
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